1. Field of the Invention
The present invention relates to a suction pad for attracting a work or holding the work after the work is attracted, in such a way as to enable the work to be fed to a predetermined position.
2. Description of the Related Art
There has heretofore been used a suction cup or pad coupled to a vacuum suction source in order to feed, for example, a thin plate-shaped work to a desired position.
FIG. 1 shows this type of suction pad. More specifically, a suction pad 2 employed in a prior art comprises a base 4 and a suction skirt 6. In addition, the suction pad 2 has a through hole 8 defined therein, which extends from the base 4 to the inside of the suction skirt 6. If an unillustrated vacuum suction source is energized when it is desired to feed a work W, the inside of the skirt 6 of the suction pad 2, which abuts against the work W, is subjected to the vacuum, so that a peripheral edge 6a of the suction skirt 6 adheres closely to the work W.
The suction pad 2 which has adhered closely to the work W in this way is displaced by, for example, an arm of an unillustrated robot so as to feed the work W in a predetermined direction in unison with each other.
In order to release the work W from the suction pad 2 after the work W has been attracted by the suction pad 2 and fed in the predetermined direction, compressed air is introduced into the skirt 6 of the suction pad 2 through the through hole 8 of the base 4 coupled to the vacuum suction source so as to release the inside of the skirt 6 from the vacuum. As a result, the work W is moved away from the suction pad 2.
In a case where a work W with a very smooth surface, such as metal, glass, etc., is attracted and held by the suction pad 2, however, if the suction pad 2 is formed of synthetic rubber or the like, the skirt 6 has an adhesive force, and hence the attracting force of the suction pad 2 with respect to the work W is extremely great. In other words, the degree of adhesion between the suction pad 2 and the work W becomes greater. Therefore, when it is desired to release the work W from the suction pad 2, the compressed air is slow to enter an attraction or suction surface of the skirt 6, i.e., between the skirt 6 of the suction pad 2 and the work W, thereby requiring much time to release the work W from the suction pad 2.
As shown in FIG. 1, the thickness of the leading end 6a of the skirt 6 of the suction pad 2 is thinner than that of each of other portions thereof as mentioned above. Thus, when air in the skirt 6 is drawn, respective attracting portions of the leading end 6a with respect to the work W are often deformed by the vacuum.
When a large-diameter suction pad 2 is used, there is observed a phenomenon that undesired or improper sound is produced, by pressing such a suction pad 2 against the work W and forcing out air from the inside of the skirt 6 at the time that the work W is attracted by the suction pad 2. Specifically, when the circumferential leading end 6a of the skirt 6 is brought into contact with the work W so as to make an airtight state therebetween and the suction pad 2 is pressed against the work W under this condition, the compressed air in the suction pad 2 is forced to escape at some point in time. Consequently, the thin-wall portion of the leading end 6a of the suction skirt 6 vibrates to produce undesired or improper sound. The sound which is produced at regular intervals while the work W is being attracted and held by the suction pad and being fed to a predetermined direction, impairs the working environment and produces a cause of noise pollution.
In order to feed a printed circuit board with ICs mounted thereon, for example, the quality of the material of each suction pad and the size thereof must be selected according to the type and size of each work as in a case where a conductive suction pad is used as a destaticizing countermeasure.
In this case, the quality of the material of the suction pad cannot be identified with ease from its appearance. Therefore, paint is applied on the surface of the suction pad and the quality of its material is indicated thereon.
The above-described prior art has, however, the problem that when the attraction of the work W by the suction pad is carried out, a flexible resin body constituting the suction skirt is expanded and shrunk and the paint applied onto the surface of the suction pad is gradually separated from its surface, so that characters, symbols, etc. cannot be identified.